Fix crash when user closes window prior to the "Confirm Install" prompt showing

chrome/browser/ui/cocoa/native_window_deletion_observer_cocoa.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_COCOA_NATIVE_WINDOW_DELETION_OBSERVER_COCOA_H_
+#define CHROME_BROWSER_UI_COCOA_NATIVE_WINDOW_DELETION_OBSERVER_COCOA_H_
+
+#include "base/mac/scoped_nsobject.h"
+#include "chrome/browser/ui/native_window_deletion_observer.h"
+
+@class BridgedNativeWindowDeletionObserver;
+
+class NativeWindowDeletionObserverCocoa : public NativeWindowDeletionObserver {
+ public:
+  explicit NativeWindowDeletionObserverCocoa(gfx::NativeWindow window);
+  ~NativeWindowDeletionObserverCocoa() override;
+
+  // NativeWindowDeletionObserver:
+  bool IsNativeWindowAlive() const override;
+
+ private:
+  base::scoped_nsobject<BridgedNativeWindowDeletionObserver> bridge_;
+
+  DISALLOW_COPY_AND_ASSIGN(NativeWindowDeletionObserverCocoa);
+};
+
+#endif  // CHROME_BROWSER_UI_COCOA_NATIVE_WINDOW_DELETION_OBSERVER_COCOA_H_